The present invention relates to integrated circuits and methods for keeping track of the power history of a system or subsystem.
Many high-reliability systems, and particularly military systems, will use a special electrolytic device (a "sodium cell") to measure accumulated time under power. By inspection of this device, maintenance technicians can determine when an electronic component has exceeded its rated time in service. However, because this component must be visually inspected, it is not widely used in other types of systems.
The integrated circuit of the presently preferred embodiment includes not only a real time clock, but also an elapsed time counter and a third counter. The elapsed time counter measures the total number of seconds during which a system has been powered up. The third counter is a "cycle counter," which measures the number of times a power cycle (power-up and power-down) has occurred. Thus, by reading the cycle counter and the elapsed time indicator, the general power history of a system can readily be determined, even if the system itself has totally failed. This integrated circuit, in the presently preferred embodiment, is battery backed, and is advantageously combined with a system for which power history must be maintained.
The presently preferred embodiment contains also contains a large number of other innovative features, which are described in detail in the accompanying specification. However, it must be understood that the claimed inventions can be practiced without the other disclosed innovations (although some such alternative embodiments may not confer the full benefits of the preferred embodiment).